Calling it "the biggest change to iOS since the introduction of the iPhone," Apple CEO Tim Cook on Monday unveiled an operating system for iPhones and iPads that will radically overhaul how users' touchscreens look.

The new system, iOS 7, was part of a two-hour presentation that included refreshed MacBook Airs, the announcement of an iTunes Radio streaming-music service and a sneak peek at a new Mac Pro that will be the most powerful computer Apple has ever made.